Polyvinyl chloride-polymethacrylonitrile interpolymer processing air for polyvinyl chloride

ABSTRACT

Interpolymers especially useful as processing aids for polyvinyl chloride (PVC) are prepared by polymerizing vinyl chloride in the presence of polymethacrylonitrile (PMAN) or by polymerizing methacrylonitrile in the presence of polyvinyl chloride. In a preferred method, a conventional PVC polymerization is halted at or near its completion, unreacted monomer is removed, a minor proportion up to about 50 percent of methacrylonitrile (MAN) monomer, based on the weight of the interpolymer, is added and the reaction continued until the MAN polymerizes. The PVC-PMAN interpolymer recovered from such a system is an effective aid in processing conventional PVC, or it can be used per se since it is readily processable by calendering or extruding.

ilnited States Patent Yu et al.

[54] POLYVINYL CHLORIDE- POLYMETHACRYLONITRILE INTERPOLYMER PROCESSINGAIR FOR POLYVINYL CHLORIDE Inventors: Arthur J. Yu, Stamford, Conn; PaulKraft, Spring Valley, NY.

Assignee: Stauffer Chemical Company, New

York, NY.

Filed: Dec. 4, 1969 Appl. No.: 882,326

1m. 01. ..cosr 29/24, cosr 29/56 1 Field of Search ..260/876, 881

References Cited UNITED STATES PATENTS 4/1965 VanEssen et al. ..260/8815/1962 Landler et al. ..260/8 8l 5/1966 Magat et al ..260/881 1/1967Heaps ..260/876 3/1970 Williams ..260/876 l vs. C: ..260/876 R, 260/296AN, I

[ 1 Aug. 22, 1972 FOREIGN PATENTS OR APPLICATIONS 38/6644 5/1963 Japan..260/881 622,897 6/1961 Canada ..260/881 932,852 7/1963 Great Britain..260/876 Primary Examiner-Samuel H. Blech Attorney-Wayne C. Jaeschke,Martin Goldwasser, Paul J. Juettner and Daniel S. Ortiz [57] ABSTRACTlnterpolymers especially useful as processing aids for polyvinylchloride (PVC) are prepared by polymerizing vinyl chloride in thepresence of polymethacrylonitrile (PMANlor by polymerizingmethacrylonitrile in the presence of polyvinyl chloride. in a preferredmethod, a conventional PVC polymerization is halted at or near itscompletion, un-

11 Claims, No Drawings POLL CHLOREDE- l l i "ril; E I r PROCESSHNGFORPOL" i i w BACKGROUND OF 'THE INVENTION When processing polyvinylchloride, the resin undergoes a fluxing step after which it isfabricated into its desired shape. During this time, the resin mustremain stable at the processing and fluxing temperatures. Additionally,the resin must yield under stress, it must have adequate flow propertiesand it must lend itself to milling and extrusion. Since polyvinylchloride usually does not itself possess these properties, it has beennecessary or desirable to add various processing aids to the resin. Forinstance, pure acrylic polymers in granular form are dry-mixed with thePVC resin and then milled on a calender or extruded. Alternatively, itis suggested by British Pats. Nos. 1,062,308 and 1,015,334 that thevinyl chloride may be polymerized in the presence of a preformed acrylicpolymer or that an acrylic monomer may be added to the polyvinylchloride latex and polymerized in situ. Specifically, recommended foruse in this matter are alkyl acrylates or methacrylates, styrenes andacrylonitrile. The resulting product is an emulsion grade, porouspolyvinyl chloride blended with the polyacrylate modifier. Such modifiedpolymers and processing aids permit faster calendering with improvedgloss, better surface qualities on extrusion, freedom from plating,improved flow and other benefits. However, they must be used in rathersubstantial proportions when combined with the PVC which is to beprocessed and the resulting blends must be milled quite intensively inorder to achieve these benefits.

Thus, it is among the objects of this invention to provide new and moreefficient processing aids for polyvinyl chloride which can be used atlower concentrations. A particular object is to provide, for the firsttime, a simple method whereby a certain acrylic polymer can be combinedwith PVC which has been made by either an emulsion or suspensionpolymerization technique, thereby desirably modifying the processingcharacteristics of the resulting resin.

BRIEFDES ONOFTHEINVENTION These and other objects are achieved by theprocess of this invention which broadly comprises forming aninterpolymer of polyvinyl chloride and polymethacrylonitrile. The amountof polymethacrylonitrile in the interpolymer can range from 1 to 99percent, by weight, with the balance of the interpolymer being PVC; thepreferred range of PMAN being about 20 to 50 percent, by weight. It isindeed surprising that these desirable interpolymers, as well as theirpolyblends with PVC, can be achieved only by the use ofmethacrylonitrile. Thus, acrylonitrile, for instance, is entirelyinoperable in the process of this invention. It is also surprising thatthe full advantages of this invention are not realized by simplycopolymerizing a mixture of vinyl chloride and methacrylonitrile.Moreover, we have found that physically mixing PVC and PMAN is a ratherdifficult and time consuming process which requires the use of highconcentrations of the costly PMAN and of added stabilizers in order toachieve a suitable product. Although such an approach is feasible, it isnot a desirable method of improving the processibility of PVC ascompared with the novel process of this invention as set forthhereinbelow. Thus, it is necessary, rather, that either of thesemonomers, i.e. either vinyl chloride or methacrylonitile, be firstpolymerized whereupon the second monomer, i.e. the vinyl chloride or themethacrylonitrile, must then be polymerized in the presence of theinitially preformed polymer. Apparently, the second monomer is absorbedby and polymerized within the particles of the initially preformedpolymer and thereby produces a modified PVC resin which serves as aneffective processing aid for blending with additional polyvinyl chlorideor which can be processed per se without the addition of any otherprocessing aid.

This invention is therefore seen to relate to interpolymers of PVC andPMAN as well as their preparation and use. More specifically, it relatesto interpolymers of polyvinyl chloride and polymethacrylonitrile as wellas the polyblends of these interpolymers with PVC. It has been found,unexpectedly, that these PVC-PMAN interpolymers function as PVCprocessing aids with the major advantage that they can be used at lowerlevels of methacrylonitrile than is possible with the usual commercialpolymethyl methacrylate-polyethyl acrylate (PMMA-PEA) processing aids.

DETAILED DESCRIPTION OF THE INVENTlON According to a preferred specificembodiment of this invention, polyvinyl chloride or a copolymer of vinylchloride with a minor proportion of vinyl acetate is first prepared byconventional suspension polymerization procedures whereupon unreactedvinyl chloride is removed from the system after the polymerization is atleast about 60 percent complete. A proportion of a second, i.e. anactive, monomer system containing methacrylonitrile in an amount suchthat the resulting interpolymer will contain at least 1 percent and nomore than about 99 percent by weight of MAN, is then added. This secondmonomer system can contain methacrylonitrile alone or in admixture withup to about 50 percent, by weight, of the second monomer system, of oneor more ethylenically unsaturated monomers. The polymerization isthereupon continued until this active monomer or monomer mixture ispolymerized.

In the resulting interpolymer, the polymethacrylonitrile, or copolymerthereof, comprises from about 1 to about 99 percent, by weight, andpreferably from about 20 to 50 percent, by weight, of its total solidscontent while the polyvinyl chloride comprises from about 1 to 99percent and preferably from about 50 to percent, by weight, of theresulting interpolymer. it is important that the active or secondmonomer system which is employed consist preferably of about 50 to 100percent, by weight, of methacrylonitrile. However, as a minor componentof this active or second monomer system, up to about 50 percent, byweight, and preferably from about 5 to 25 percent, by weight, of thesecond monomer system may consist of one or more monomers selected fromthe group consisting of vinylidene chloride; acrylonitrile; vinylchloride; the C C alkyl esters of methacrylic acid such, for example, asmethyl, ethyl, n-propyl and iso-propyl methacrylate; glycidylmethacrylate; and the C, C or higher alkyl esters of acrylic acidwherein the alkyl group may be straight or branched such, for example,as methyl, iso-propyl, 2-ethylhexyl or lauryl acrylate. Especiallypreferred are second monomer systems containing -75 to 95 percent, byweight, of methacrylonitrile with 5 to 25 percent, by weight, of methylmethacrylate, methyl acrylate, ethyl methacrylate, ethyl acrylate,and/or glycidyl methacrylate. Thus, one or more of these optionalethylenically unsaturated monomers may be present in the resultinginterpolymer in a concentrationof up to about 49.5 percent of its totalweight.

It has been found that by intimately admixing minor proportions of theinterpolymer processing aids thus obtained with polyvinyl chlorideresins, the resultant mixtures are substantially easier to process thanthe unmodified polyvinyl chloride. Possible concentrations of the newinterpolymers in these polyblends are such that the polyvinyl chloride,whether derived from the interpolymer or from the PVC being modified, ispresent in a total concentration of from about 51 to about 99 percent,by weight, while the balance of from about 49 to 1 percent, by weight,of the polyblend is the PMAN or a copolymer of MAN with one or more ofthe above described ethylenically unsaturated monomers. A preferredembodiment comprises polyblends in which the concentration of PMAN orits copolymers is from about 2 to 15 percent of the total weight of thepolyblend. When evaluated in a Brabender plastograph, the resulting easyprocessing polyblends are characterized by their shortened flux times.The PMAN-modified PVC processing aids which contain the proportions ofbetween about 20 and 50 percent, by weight, PMAN and from about 50 to 80percent, by weight, of polyvinyl chloride, offer a decided advantageover PVC processing aids which comprise polymers of lower alkyl acrylicacid esters. -Where the resulting interpolymer contains less than aboutpercent, by weight, of PMAN or of a MAN copolymer, it may be used, perse, as an easy processing resin.

The preferred process of this invention comprises adding the appropriateamount of methacrylonitn'le to an aqueous suspension of polyvinylchloride, particularly PVC obtained by suspension polymerization andhaving an average particle size of from about 5 to 150 microns andpreferably about 25 to 80 microns. The particle size of the PVC is animportant consideration in the process of this invention. The reason forthis is not entirely understood but is believed to relate to the factthat the methacrylonitrile is, in some vmanner, more readily absorbed byPVC particles whose particle size is substantially within the abovespecified range and thus polymerizes more effectively. Polymerization ofthe MAN is initiated by a standard oil-soluble catalyst which may beeither already present in the suspension or which may be freshly addedto it. The particular catalyst, temperature, reaction time and otheroperating conditions which are chosen are, of course, interdependent andmay be those usually employed in the polymerization of acrylic monomersof this type. A chain transfer agent may be used, if desired, but it isnoteworthy that such an agent is not required as is often found to benecessary in prior art processes in this field. Other variations inpolymerization technique will suggest themselves to those skilled in theart.

The process of this invention is particularly useful with polyvinylchloride homopolymers but there can also be employed the usualcopolymers of vinyl chloride with minor proportions of vinyl acetateprovided that such copolymers are within the above specified particlesize range. Similarly, the processing aids resulting from this novelprocess are especially desirable for incorporation in PVC as well as invinyl chloride-vinyl acetate copolymers which, as is known, are quitedifiicult to calender.

For reasons of economy and efficiency, it is preferable that the PVC beinitially polymerized until the reaction is at least about 60 percentand, preferably about percent or more complete. Unreacted vinyl chloridemust then be removed when the system is vented before the MAN, or MANcomonomer mixture, can be added and polymerized. If this is not done,the remaining vinyl chloride monomer will undergo an undesirablecopolymerization with the MAN. This utilization of sequentialpolymerization, i.e. of first polymerizing one of the monomers prior tointroducing and then polymerizing the other, is a unique and importantaspect of the process of this invention. The methacrylonitrilepolymerization may be carried out in the same vessel immediately afterthe vinyl chloride polymerization is completed or the PVC may have beenpreviously prepared, stored and then used in this process. However, ifthe MAN, or MAN comonomer mixture, polymerization is carried out in situas soon as the PVC system has been vented and unreacted monomer removed,it may not be necessary to add any additional catalyst.

When PVC is the major component of these new interpolymers, it isgenerally preferred to first polymerize the vinyl chloride and to thenpolymerize the methacrylonitrile in its presence. However, the reversesequence is equally feasible, i.e., first forming thepolymethacrylonitrile, or a copolymer of MAN with a C -C alkylmethacrylate ester, glycidyl methacrylate or a C C alkyl acrylate esterremoving unreacted MAN and any other unreacted monomers, and thenpolymerizing the vinyl chloride in the presence of the PMAN or MANcopolymer. Here again, the second polymerization step may followimmediately in situ, or a preformed PMAN or MAN copolymer may be storedand used at a later date.

The following examples will further illustrate the embodiment of thisinvention. In these examples, all parts given are by weight unlessotherwise noted.

EXAMPLE I An autoclave was charged with 210 parts, by weight, ofsuspension grade polyvinyl chloride resin (Rel. Visc. of 2.02 asdetermined in a 1 percent, by weight, cyclohexanone solution at 25 C.)having a particle size between about 50 and 80 microns, 900 parts ofdeionized water, parts of methacrylonitrile and, as a catalyst, 0.27parts of 2,2'-azobisisobutyronitrile. The autoclave was heated to 85 C.and agitated at this temperature for three hours. A second additioncomprising 0.27 parts of the latter catalyst was then made and thetemperature was increased to C. and maintained at this level for onehour. The reactor was then cooled and the contents collected viafiltration. The resultant interpolymer was then dried overnight in anoven set at 50 C.

Conversion 90 percent of the polymethacrylonitrile. Composition, basedon conversion of MAN to polymer 27.8 percent. PMAN/72.2 percent PVC, byweight.

This PVC/PMAN interpolymer was compared (1) with a sample of PVC whichhad not been admixed with a processing aid; (2) with a sample of PVC towhich this PVC/PMAN interpolymer had been added; and (3) with a sampleof PVC containing a commercial processing aid (K-l 20-N, Rohm and Haasbrand name for a copolymer of about 90 percent methyl methacrylate andpercent ethyl acrylate). The results of this comparison showed that thenovel composition of this invention could be used as a processing aid ata substantially lower concentration level than was possible with thecommercial processing aid while still providing desirable millingcharacteristics to the PVC as evidenced by its good gloss and clarity.

EXAMPLE II The polymerization procedure of Example I was repeated using210 parts, by weight, of suspension grade PVC which was substantiallyfree of unreacted monomer and having a particle size between about 50and 80 microns. It was conducted in 900 parts of water and involved theaddition of 90 parts of a monomer mixture consisting of 90 percent, byweight, of MAN and 10 percent, by weight, of methyl methacrylate. Themonomer mixture was rapidlyabsorbed into the PVC phase while it wasstirred and heated at 90 C. After 2 hours, the monomer mixture wasessentially polymerized within the host polymer and the resultinginterpolymer product analyzed as a 76 percent PVC :24 percent PMAN-PMMAinterpolymer. This material served as an effective processing aid forpolyvinyl chloride resin at a concentration level which was onlyone-half the total concentration of an acrylic ester polymer of the typefound in a commercial PMMA- PEA processing aid.

MANto EXAMPLE III The procedure of Example II was repeated with theexception, in this instance, that the 90:10 MANzMMA monomer mixture wasreplaced, respectively, with: (a) a mixture of 90 percent MAN and 10percent ethyl acrylate; (b) a mixture of 85 percent MAN and percentglycidyl methacrylate; (c) a mixture of 95 percent MAN and 5 percentethyl methacrylate; and (d) a mixture of 50 percent MAN and 50 percentmethyl acrylate. In each instance, the resulting interpolymer wasincorporated into a rigid PVC formulation at concentration levels suchthat the resulting polyblends contained, respectively, 3 and 10 percentof the MAN copolymer as based on the total weight of the polyblends.These interpolymers were then compared with a commercially availablelower alkyl acrylic acid ester polymer processing aid at equivalentacrylic ester polymer levels and, under standard milling conditions, theproducts of this invention exhibited improved behavior both on the milland in the finished sheets.

EXAMPLE IV The procedure of Example I was repeated three times usingmixtures of PVC and MAN whose proportions, by weight, were,respectively, PVC:15 MAN, 50 PVC:5O MAN and 60 PVC:40 MAN. In each case,useful processing aids comparable to the product of Example I wereobtained.

EXAMPLE V An autoclave was charged with 197 parts of monomeric vinylchloride, 0.13 parts of 2,2'-azobisisobutyronitrile, 435 parts ofdeionized water, 75 parts of a 1 percent aqueous solution of methylcellulose and 3 parts of a previously prepared methacrylonitrilezmethylmethacrylate (:5) copolymer. The temperature of the reactor wasmaintained at 60 C. while agitation was simultaneously applied at a rateof 41 rpm throughout the entire 10 hour reaction period. The reactor wasthen cooled and the contents collected via filtration. The resultantinterpolymer was then dried overnight in an oven set at 50 C.

Conversion was calculated as 94 percent of vinyl chloride to PVC and theproduct was analyzed at a 98.5 percent PVC: 1 .5 percent PMAN-PMMAinterpolymer. It was found to provide excellent results, per se, as aneasy processing resin.

EXAMPLE VI An autoclave was charged with 197 parts of monomeric vinylchloride, 0.13 parts of 2,2'-azobisisobutyronitrile, 435 parts ofdeionized water, 40 parts of 1 percent aqueous solution of methylcellulose, and 3 parts of a previously prepared methacrylonitrilezmethylmethacrylate (95:5) copolymer. The temperature of the reactor wasmaintained at 60 C. while agitation was simultaneously applied at a rateof 48 rpm throughout the entire 10 hour reaction period. The reactor wasthen cooled and the contents collected via filtration. The resultantinterpolymer was then dried overnight in an oven set at 50 C. Conversionwas calculated as percent of vinyl chloride to PVC and the product wasanalyzed as a 98.5 percent PVC:l.5 percent PMAN-PMMA interpolymer. Itwas found to provide excellent results, per se, as an easy processingresin.

Variations may be made in proportions, procedures and materials withoutdeparting from the scope of this invention as defined in the followingclaims.

What is claimed is:

1. An interpolymer comprising from about 1 to 99 percent, by weight, ofa polymer selected from the group consisting of polyvinyl chloride andcopolymers of vinyl chloride with a minor proportion of vinyl acetateand from about 1 to 99 percent, by weight, of a polymer selected fromthe group consisting of polymethacrylonitrile and copolymers ofmethacrylonitrile with up to about 25 percent, by weight, of at leastone monomer selected from a group consisting of vinylidene chloride,vinyl chloride, acrylonitrile, glycidyl methacrylate, the C -C alkylmethacrylate esters, the C -C alkyl acrylate esters and mixturesthereof; said interpolymer resulting from the suspension polymerizationof vinyl chloride in the presence of a previously prepared aqueoussuspension of a substantially monomer free polymer selected from thegroup consisting of polymethacrylonitrile and copolymers ofmethacrylonitrile with up to about 25 2. A method for the preparation ofinterpolymers of polyvinyl chloride and polymethacrylonitrile whichcomprises the steps of: (l) preparing, by means of a suspensionpolymerization procedure, a substantially monomer free polymer ofmethacrylonitrile; (2) polymerizing vinyl chloride by means of asuspension polymerization procedure in the presence of themethacrylonitrile polymer resulting from step (1); and (3)recovering'the interpolymer of polyvinyl chloride andpolymethacrylonitrile thereby obtained.

3. The method of claim 2, wherein said polymer of methacrylonitrilecomprises from at least about 50 to 100 percent, by weight, ofmethacrylonitrile together with from about 50 to percent, by weight, ofat least one other ethylenically unsaturated monomer.

4. The method of claim 2, wherein the concentration of vinyl chloridewith respect to the polymer of methacrylonitrile resulting from step(1), is such that the resulting interpolymer contains from about 1 to 99percent, by weight, of vinyl chloride.

5. The method of claim 3, wherein said methacrylonitrile and saidethylenically unsaturated monomer are in the relative proportions offrom about 50 to about 95 percent, by weight, of methacrylonitrile toabout 50 to about percent of said ethylenically unsaturated monomer.

6. The method of claim 2, wherein the vinyl chloride polymer prepared instep (2) is a copolymer of vinyl chloride with a minor proportion ofvinyl acetate.

7. The method of claim 3, wherein said ethylenically unsaturated monomeris selected from the group consisting of vinylidene chloride, vinylchloride, acrylonitrile, glycidyl methacrylate, the C C alkyl esters ofmethacrylic acid, the C -C alkyl esters of acrylic acid and mixturesthereof.

8. The interpolymer resulting from the process of claim 2.

9. A method for the preparation of processing aids for polyvinylchloride, which comprises suspension polymerizing vinyl chloride in thepresence of an aqueous suspension of substantially monomer freepolymethacrylonitrile.

10. The method of improving the processability of polyvinyl chloride,which comprises preparing a polyblend by mixing said polyvinyl chloride,prior to processing, with an interpolymer produced by the process ofclaim 2 in suflicient amount to provide between about 1 and about 49percent of polymethacrylonitrile based on the total weight of theresulting polyblend.

11. A polyblend comprising polyvinyl chloride in physical admixture witha minor proportion of an interpolymer consisting essentially of fromabout 1 99 percent, by weight, of a polymer selected from the groupconsisting of polyvinyl chloride and copolymers of vinyl chloride with aminor proportion of vinyl acetate together with from about 99 1 percent,by weight, of a second polymer which is selected from the groupconsisting of polymethacrylonitrile and copolymers of methac lonitrilewith u to about 25 ercent, b weighn of at least one r honomer selecte%from th group consisting of vinylidene chloride, vinyl chloride,

acrylonitrile, glycidyl methacrylate, the C,C alkyl methacrylate esters,the C -C, alkyl acrylate esters and mixtures thereof; said interpolymerresulting from the suspension polymerization of vinyl chloride in thepresence of a previously prepared aqueous suspension of a substantiallymonomer free polymer selected from the group consisting ofpolymethacrylonitrile and copolymers of methacrylonitrile with up toabout 25 percent, by weight, of at least one monomer selected from thegroup consisting of vinylidene chloride, vinyl chloride, acrylonitrile,glycidyl methacrylate, the C C alkyl methacrylate esters, the C C, alkylacrylate esters and mixtures thereof.

2. A method for the preparation of interpolymers of polyvinyl chlorideand polymethacrylonitrile which comprises the steps of: (1) preparing,by means of a suspension polymerization procedure, a substantiallymonomer free polymer of methacrylonitrile; (2) polymerizing vinylchloride by means of a suspension polymerization procedure in thepresence of the methacrylonitrile polymer resulting from step (1); and(3) recovering the interpolymer of polyvinyl chloride andpolymethacrylonitrile thereby obtained.
 3. The method of claim 2,wherein said polymer of methacrylonitrile comprises from at least about50 to 100 percent, by weight, of methacrylonitrile together with fromabout 50 to 0 percent, by weight, of at least one other ethylenicallyunsaturated monomer.
 4. The method of claim 2, wherein the concentrationof vinyl chloride with respect to the polymer of methacrylonitrileresulting from step (1), is such that the resulting interpolymercontains from about 1 to 99 percent, by weight, of vinyl chloride. 5.The method of claim 3, wherein said methacrylonitrile and saidethylenically unsaturated monomer are in the relative proportions offrom about 50 to about 95 percent, by weight, of methacrylonitrile toabout 50 to about 5 percent of said ethylenically unsaturated monomer.6. The method of claim 2, wherein the vinyl chloride polymer prepared instep (2) is a copolymer of vinyl chloride with a minor proportion ofvinyl acetate.
 7. The method of claim 3, wherein said ethylenicallyunsaturated monomer is selected from the group consisting of vinylidenechloride, vinyl chloride, acrylonitrile, glycidyl methacrylate, theC1-C3 alkyl esters of methacrylic acid, the C1-C12 alkyl esters ofacrylic acid and mixtures thereof.
 8. The interpolymer resulting fromThe process of claim
 2. 9. A method for the preparation of processingaids for polyvinyl chloride, which comprises suspension polymerizingvinyl chloride in the presence of an aqueous suspension of substantiallymonomer free polymethacrylonitrile.
 10. The method of improving theprocessability of polyvinyl chloride, which comprises preparing apolyblend by mixing said polyvinyl chloride, prior to processing, withan interpolymer produced by the process of claim 2 in sufficient amountto provide between about 1 and about 49 percent of polymethacrylonitrilebased on the total weight of the resulting polyblend.
 11. A polyblendcomprising polyvinyl chloride in physical admixture with a minorproportion of an interpolymer consisting essentially of from about 1 -99 percent, by weight, of a polymer selected from the group consistingof polyvinyl chloride and copolymers of vinyl chloride with a minorproportion of vinyl acetate together with from about 99 - 1 percent, byweight, of a second polymer which is selected from the group consistingof polymethacrylonitrile and copolymers of methacrylonitrile with up toabout 25 percent, by weight, of at least one monomer selected from thegroup consisting of vinylidene chloride, vinyl chloride, acrylonitrile,glycidyl methacrylate, the C1-C3 alkyl methacrylate esters, the C1-C12alkyl acrylate esters and mixtures thereof; said interpolymer resultingfrom the suspension polymerization of vinyl chloride in the presence ofa previously prepared aqueous suspension of a substantially monomer freepolymer selected from the group consisting of polymethacrylonitrile andcopolymers of methacrylonitrile with up to about 25 percent, by weight,of at least one monomer selected from the group consisting of vinylidenechloride, vinyl chloride, acrylonitrile, glycidyl methacrylate, theC1-C3 alkyl methacrylate esters, the C1-C12 alkyl acrylate esters andmixtures thereof.